1. Field of the Invention
The present invention relates to a through-hole forming method, inkjet head, and silicon substrate.
2. Description of the Related Art
There has been studied a technique of forming a through-hole in a silicon substrate by isotropic or anisotropic etching and applying it to a variety of devices. This technique is also applied to formation of the ink supply port of an inkjet head.
When forming an inkjet head, especially when arranging many inkjet head printing elements on one substrate, the edge position of a through-hole on the etching end side is sometimes misaligned with the positions of an inkjet printing element and ink orifice. As a result, the printing characteristics of the nozzles of the inkjet head vary, greatly degrading the quality of a printed image.
To solve this, the present inventor has proposed a method of controlling the size of a through-hole by forming a heavily doped region around a region where the through-hole is formed in a silicon substrate (see Japanese Patent Laid-Open No. 2004-34533).
However, according to the method disclosed in Japanese Patent Laid-Open No. 2004-34533, when the heavily doped region is thin, the mechanical strength is poor. As shown in FIG. 4, warpage or a crack occurs under the stress between the heavily doped region and an etch stop layer. Thickening the heavily doped region can suppress generation of warpage, but decreases productivity and raises the cost.